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A. E. KEITH TELEPHONE EXCHANGE SYS TEM Original Filed May 14, 1.907 10 Sheets-Sheet 2 .pril 13,1926. a l Re, 16,316

A. E. KEITH -TELEPHONE xcmms sysran A' Origlngl Filed May 14, 1907 10 Sheets-Sheet 3 m 9 1 3 l .lm A

original Filed May' 14 1907 10 Sheets-Sheet 5 INI Re, l 6,316

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April 13 1926.

" vA. E. KEITH TELEPHONE EXCHANGE SYSTEM 10 Sheets-smeet` 10 JK OOQ )N @E @WWW v VAV Aiwa... www @fu n@ @R W HHHYH Original Filed May 14. 1907 y To all whom itmy concern:

Reissued Apr. 13, 1926.

UNITEDA STATES PATENT oFFlcE.

ALEXANDER E. KEITH, 0F HINSDALE, ILLINOIS, ASSIGNOR, BY MESNE ASSIGNMENTS, TO AUTOMATIC ELECTRIC INC., 0F CHICAGO, ILLINOIS, A CORPORATION OF DELAf WARE.

TELEPHONE-EXCHANGE SYSTEM.

Original No. 1,217,121, (hted February 20, 1917, Serial N0. 373,649, led Hay 14, 1907. Application for reissue led Hay 23, 1918. Serial Fo. 286,249.

Be it known that I, ALEXANDER E. KEITH, a citizen of the United States of America, and a resident of Hinsdale, Du Page County, and State of Illinois, have invented a certain new and useful Improvement in Telephone-Exchange Systems, of which the folv lowing is a specification. My invention relates to telephone systems in general, but more particularly to automatic or semi-automatic-telephone exchange systems, and especially to systems in which either all or a portion of the eneral operation of connecting calling te ephone lines with called lines is accomplished automatically-that is to say, by means of selecting or connecting switches controlled from some distant point, as distinguished from ordinary manual switchboards.

Generally stated' he object of my inven-4 tion is the provision of an improved yand highly elicient telephone exchange system.

Special objects are theprovision of means whereby the connectors or final numerical switches may be considerably reduced in number. without reducing the eiiiciency of the service; the provision of a novel arran 'ement whereby eachk subscriber is provi ed with two individual trunking switches, one by which the subscriber calls other Subscribers, and another by which the subscriber is called by other subscribers; the provision of a novel and eiiicient arrangement by which intermediate nonnumerical trunk selectors are employed for automatically vselecting idle numerical switches, such as connectors or other similar swltches; the provision of an arrangement by whlch, after several switches have been brought into serv tion, and a new or'substitute connection extended back from thecalled telephone line in the direction of the calling subscriber, the disrupting or breaking down ofthe primary or temporary connectlon being simultaneous or practically simultaneous with the establishment of the new or talking connection; and the provision of certain details andvfeatures of improvementv andv combinations tending to increase the general etliciency and serviceability of a telephone system of this particular character.

To the foregoing and other useful ends, provide certain features of construction and novel arrangements which constitute a substantial contrlbution to the general art of telephony, particularly the art ofautomatictelephony, and which point the way to a new line of development, as will hereinafter more fully. appear. l

In the accompanyingdrawings Figure 1 represents diagrammatically a subscribers substation A and its allotted line switch C, with the master switch D, a battery B having its positive terminal grounded at G, provided for loperating the line and master switches.

Fig. 2 shows diagrammatically a first-selector switch E and a Lsecond-selector switch F, in connection with which I have electedto explain my invention.

Fig.r 3 shows diagrammatically a connector switch H of an; improved type, a secondary or trunking line switch I, together with its'master switch J. Y

I1`ig. 4 shows a called subscribers substation A connected with the outgoing line switch C', and also with a second or incoming line switch K of an improved type;

The'switch C is controlled by the master ratus is represented in Fi s. 1, 3 and 4 while Fig. 2 represents t e main central switches.

Figs. 1, 3 'and 4, taken together, represent diagrammatically the switching apparatus involved when one subscriber of the sub-central #3300 calls another subscriber ofthe same sub-central. The switching apparatus located at this sub-central correspends to the switching apparatus located at t e other sub-centrals shown in Figs. 1, 3 and 4. Figs. 1, 3 and 4l correspond to Figs. 1, 3 and 4, respectively, like parts bein similarly shown and bearing the same re erence numerals.

Fig. 5 is a more complete diagrammatic re ntation of the line switch C.

ig. 5 is a detailed view of the construction of the bank O of the master switch D.

Figs. 6, 7, 8, 9, 10, 11 and 12 are detail views showing the various position of vthe im ulsesprings.

gig. 13 shows, in a general manner, the relative locations of the different switches employed in the system.

Y The subscriber of the sub-central #1100 may call' and signal any subscriber of the Sub-central!! #1200, #2200 and #3300 (Fig. 13) through the medium of the main central exchange. Also, if the subscriber at substation A of the sub-central #1100 desires to call another subscriber of the same subcentral, the connection is extended to the main exch and then back to the subcentral #1100 to the desired substation. In a similar manner, the subscribers of the subcentrals #1200 and #2200 may extend connection to other substations, the connection always extending through the main central excha e, even when the calling and called Subscn ers are members of the same subcentral exchange. But in the sub-central #3300 the arrangement is suchthat the subscribers may call other subscribers of the same sub-central, without loperating the main central switching apparatusthat is, the subscriber at substation A of the subcentral #3300 may call and signal the subscriber at substation A' entirely by means of switching apparatus located at the sub-central #3300, while the subscribers at subcentrals #1100, #1200 and #2200, in calli other subscribers of the same sub-centra operate switching apparatus located in the main exchange and also in theysub-centrll exchange. Furthermore, the subscribe ers of sub-centrals #1100, #1200 and #2200 'may automatically call any subscriber of the system, but the subscribers at the sub-central #3300, when they desire connection with a line outside vof their own sub-central, signal In operator at the #3300 sub-central, and theoperator, by means of a calling device, in iturn completed the connection with the The substations are all alike and may be of any suitable or approved type. The substation A, for example, comprises a receiver '2, a switch-hook for controlling the substation circuits, which controlling operations central oiiice. When the switch-hook is down the cam-arm 5 engages the spring 10, thereby bridging the ringer 11 in series with the condenser 12 across the line. Furthermore, when the switch-hook is down the said camarm 5 disengages the springs 13 and 14, thus breaking the local circuit which includes in series the primaryA winding 15, transmitter 16 and local battery 17. The substation groundk circuit is normally broken between the ground springs 18 and 19 by the camarm 6; but when the said springs are together yground is provided to the ground post 20, and to the release spring 7 as is usually the case in telephones of this type. The said substation comprises the usual 1nduction-coil 21 having the primary winding and the secondary winding 22. Being an automatic substationit is also provided with the usual and so-called vertical and rotary impulse springs 23 and 24. Said substation is, of course, provided with a dial (not shown) which is secured to the shaft 25, `together with the locking dog 26. The substation A, as shown in Fig. 1, isseen from the back, the dial being on the opposite side.

Furthermore, there is a locking cam 27 that locks the dog 26 while the receiver is on the switch-hook, to prevent a rotation oi.' the dial. For operating the impulse springs 23 and 24 the substation is provided with an impulse wheel 28 that is secured to the shaft, which impulse wheel carries on its periphery the so-called vertical impulse teeth 29 and one rotary impulse tooth 30. The said impulse teeth are so arranged that when the dial is drawn down the impulse spring 23 is not' carried into contact with the ground post 20, while the rotary spring is operated once by the rotary tooth 30 but as the dial returns, one or more of the vertical teeth engage the vertical impulse spring 23vand press it onto the said ground post 20, and after they have completed their work the rotar) impulse tooth 30, in a similar manner, again operates the rotary impulse spring 24. In this operation the subscribers rotary line conductor is first given one preliminary ground impulse and thentheV vertical linev conductor 31 is' given a number of ground impulses, after whlch the rotary line coni V-shaped member.

ducten' .32 is given one more ground impulse.' It will be noticed that as long as the dial is out of normal position the construction is such that the dog 26 permits the secondary circuit springs 33 and 34 to separate, thus preventing the impulses that are delivered to either line conductor from passing to the other. The vertical impulse spring 23 is provided withY an oblique projection or lug 268 (see Figs. 6to 12,-inclusive), on the under side of which the vertical limpulse teeth 29v are adapted to engage for driving the spring 23 intermittently onto the ground post 20. The rotary impulse spring 24 1s provided with somewhat similar-mechanism for driving the said rotary spring onto the ground post, once when the dial is rotated in one direction, and once when rotated in the opposite direction. The said rotary impulsey spring 24 hasy on its under side a V-shaped member 269 having `two sides c and d, and thereis in addition an auxiliary spring 270 which works in: conjunction with thev said As shown inore'clearly in Fig. 6 the auxiliary spring 270 is provided with a lower curved parte having the rear' section 271 curving outwardly, as shown alsoin Figs. 7,' 8, 9, 10, 11 and 12. The front section 272 of said member e is designed to fall just below the apex of the V-shaped member 269, so that the rotary impulse tooth 30, whenmoved in thc-direction of the arrow (Fig. 7) will pass onto the curved member e, thus Ypressing the rotary impulse spring 24 onto the ground post 20 for a comparatively long time, as shown in Fig. 8,y

and thus sending to the line a comparativelyl long' impulse. As the impulsel wheel advan thev vertical impulse teeth 29 approach the lug 268 of the vertical impulse spring23 (Fig. 8), and eventually the first tooth fthat meets the lug 268 clears the said lug, as shown in Fig. 9, but not until after the rotary impulse tooth 30 clears or disengages the curved member e.V As the impulse wheel. continues to advance in the direction of the arrow (Fig. 9), succeeding impulse teeth 29 will clear the projection 268, Aas shown in Fig. 10. Then when the impulse wheely is released, first the vertical impulse spring* 23, which the vertical impulse teeth previously cleared, is carried intoreiigagement vvwith theigroundpost 20, as indicated in Figli-5 and' as the impulse wheel nears its normal position therotary impulse tooth 30`passes under'the curvedl member c of the auxiliary spring 270 (Fig. 12), engaging the y V-sli'aped member 269' directly, but for a time only, sending the ordinary inithrougli themedium of the rotary iinp'uls'e 'spring 24, to the line conductor 32, after Awhich the said. member 269 is cleared, as 'shownfin Fig. 7, as the impulse wheel reaches its normal position. v, The operations,

asthus'describ'ed, 'are' repeated each time that the dial is operated, and the number ofvimpulses produced'through the medium of the vertical impulse spring 23 are accurately and definitely determined at each operation of the dial by the finger-hole which the subscriber previously selects on the dial. Means whereby the subscriber may signal the called subscriber comprises the push-button spring which normally engages the contact point 36; but when the button 37 is pressed the spring 35 engages the contact point 38,

whereby the vertical line conductor 31 mayv prior United States patent application, Se-

rial No. 3i1,327,fi1ed April i2, i906.

0 The said switch C comprises, as shown in 'F ig. 5, a plunger 44, plunger arm 45, bridge-cut-of relay 46, trip magnet 47 and switch-release magnet 48, all of which are built about a switch-base or frame. (not shown) of any suitable or approved design. The said switch-release magnet is provided with an armature 49 that is pivoted on a pin 5() which rises from the base of the switch. The said armature carries pivotally secured on its end a second armature 51 that is controlled by the trip magnet 47. The pin 52 about which the armature 51 oscillates is carried on the end of the armature 49.v The plunger 44 is pivotally secured by the pin 53 to the plunger arm 45, which latter is'in turn pivoted to a pin 54 that rises from vthe switch-frame- The lug 55 is stamped out of the side of the frame and is provided as a stop or rest'for the armature 49. Upon the armature 51 is secured the catch spring 56 which is adapted to engage the end 57 of the plunger arm 45. Furthermore, the said line-switch is provided with a bank of terminals, usually ten in number,ionly one of which is shown at Q (Fig. 5). As shown, thcsaid terminal Q is, for convenience of illustration, rotated from its true position with respect to the swing of the plunger 44, and the bushing 62 is Vcorrespondinglyarranged, all for the purpose of making the illustra-tion clearer. The terminal Q comprises the springs 63 and 64, 65

and 66, 67 and 68, vand 69 and 7() which are normally disconnected from each other, but which are driven into contact in the abovementioned order when the plunger 44 operates. j Normally the idle plunger 44 rests in the trough 61 ofthe plunger shaft 60.

The general operation of the switch is as follows: The trip magnetv47 is energized by a preliminary impulse, and the armature iis . n the end of the plunger arm 45 51 is attracted against the magnet cores. When the armature 51 is attracted the catch 56 slides out of contact with the end 57 of the' plunger arm 45, and the said plunger am 45, owing to the tension of the spring 58, moves about. the pin 54 and thrusts the plunger 44 into the bank terminal Q (shown m Fig. and when the trip magnet again deenergizes, the trip armature 51 falls against The switch is restored when the release magnet 48 becomes energized, whereby the armature 49 is attracted, and accordingly the trip armature 51 is ino-ved upwardly until the catch 56w slides over the end 57 then when the release magnet 48 becomes de-energ'ized the armature49 returns to normal position and remins at rest against the stop 55. Furthernmre, since the plunger arm is now in engagement with the armature 51, the. said plunger arm is also moved about the pin 54, whereby the plunger 44 is moved from the terminal Q and falls back into the trough 61 of the plunger shaft; and as the said plunger shaftis advanced keach time an idle trunk line is seized, the idle plungers are then advanced to point oppositekthe next idle trunk line. From this on the plunger 44 is carried along by the shaft GO until it is again released when another call is made.

The master switch D, which may be of any suitable or approved type, is provided for operating the plunger shaft Gt), and for ControllingA certain circuit-s that will be disf dosed hereinafter.4 It comprises the following details: A motor magnet 71 for operating the ratchet wheel 72, which latter is designed for operating thel plunger shait and a differential relay 7 3 for controlling the energizing circuit of the mbtor magnet 71. The said master switch also has a bank O comprising a plurality of individual contact segments a and a common metallic segment 74, as shown in Fig. 5. The wiper is adapted to remain in constant engagement with the bank O, and to maintain some one of the segments a in electrical connection with the common segment. 74. The wiper 75 is rated in a step-by-step manner by the rate t Wheel 72 through the medium of a 0am member 76 rigidly secured to the said wiper 75 and adapted to successively engage the pins 77, 78, 79 and 80 upon the said ratchet Wheel 72. The motor magnet 71 is provided with an amature 81 upon the end of which there is suitably secured a pawl y 82. Each time that the said magnet is energized the pawl 82 engages the ratchet wheel 72, advancing the latter one step. lt will bel noticed, therefore, that as the ratchet Wheel 72 advances in a counter-clockwise direction the wiper 75 advances step by step from right to left, and when the pin 77, ica instance,Y clears the cam 76 the retracting spring 83 restores the wiper 75 to its first position at the right of the bank O. and in enga ement with the first segment 84. The sai motor magnet 71 is provided with la couple of interrupter springs 85 andV 86 that are'included in the energizing circuit of the said motor magnet, which energizing circuit also comprises the springs 5'? and 88 controlled by the differential relay 7 3. Therefore, whenever the differential relay 73 is energized the springs 87 and S8 are pressed into contact and the motor m'agnet 71 operates step by step as long as the differential relay 73 remain-s energized. Also, it is assumed that the terminal Q. of the line switch C isv the first. terminal of the line switch bank. The plunger 44, while in normal locked engagement with the shaft 60, is retained in front of said terminal by the plu-nger shaft 60 whenever the master switch wiper 75 is in engagement withthe bank segment 84; but as the motorv magnet 71 advances the wiper 75 onto the second segment 89, thel said plunger and all idle plungers similarly engaging the shaft 60 are carried opposite the next terminal. of the line switch bank. The master switch, bank O y(Fig. 5a) comprises the individual segments a separated from. the common segni'ent 74 by the insulating strip 273. It will be noticed that after the wiper 75 passes over the segments from right to left and engagesthe last segment 164, thenpn the next step the wiper 75 passes from the extreme left contact 164 tothe contact 84 on the extreme right; but inpassing from one" extreme position to the other the upper part of the wiper 75 slides onto tlfie.l insulated member 274. This provision is made in order that the individual segments a may not'be broughtinto contact with the` com'- switch might be experienced. It should benoted that in each switch bank all of the springs 63 are permanently connected and may be made of one common piece; the springs 64, however, are individuafL-that is, there is one separate and distinct-spring for every termbinal Q, there being ten` in the bank. The springs 65,l 67, 68 and 69, like the springs 63', are also com-mon, and the springs 66 and 70, like the springs 64, are individual.r For every bank` terminal Q there is a trunk line of three conductors 90, 91 and 92 leading to a second-selector; and there is also a normal trunk line comprising the conductors 93, 94 and 96a' leading to the incoming line.. switch and a conductor leading to the connectorswitchbanks. The subscribers l'me conductors` 31 and 32 terminate in the springs 63 and 6 5 which, as has been stated, are common springs. lVhen the subscriber operatestheY line switch C and the plunger 44 engagesthe' terminal Q, the subscribers line conductors 31 and 32 are extended to the vertical and rotary trunk conductors 90 and 91 and thence to the switch E.

The selector E, shown in Fig. 2, is a modified form of the selector switch disclosed in United States Letters Patent No. 815,321,`

granted March 13, 1906, to Keith, Erickson, & Erickson. It is provided with a vertical magnet 96 and a rotary magnet 97, a release magnet 98 and a private magnet 99. The said private magnet 99, of course, controls the side switch Wipers 100, 101, 102 and 103, the said rivate magnet also controlling the circuit ofp the vertical magnet 96 in the usual manner by means of the springs 105 and 106, but not the circuit of' the release magnet, for the release magnet spring is omitted. The vertical movement of the switch shaft and, therefore, of the wipers 119, 120 and 121 is controlled by the vertical magnet 96, and the rotary movement by the rotary magnet 97, the rotary .magnet circuit being provlded with the usual interrupter springs 107. The operating magnets of the switch are, of course, controlled by the subscriber through the use of the vertical and rotary line relays 108 and 109, as is well known. Said relays have under their control the usual sprin 110, 111 and 112 and in addition the trun release springs 113 and 114, whereby the said switch may be released when the side switch wipers are in first or second position. B means of the back-release relay 115 the re ease of the switch E is brought about after the side switch has passed to third position.

Each selector switch in this system is provided wit-h line and private banks. The contacts of each line bank are adapted to be engaged by corresponding line wipers, such as the wipers 119 and 120, and the contacts of each private bank by a corresponding private wiper, such as the wiper 121.

The selector F is also a modified form of the selector of the said selector patent. It is of the brid ing type, in which the line relays 188 an 206 are ermanently connected to the side switch wipers 187 and 263. It is also provided with the vertical magnet 264* and the rotary magnet 265, the release magnet 248 and the private magnet 123.'

The line relays 188 and 206, as shown, control the so-called trunk-release springs 122 and 254, the former being connected with the trunk-release conductor 104, and the latter with the release magnet 248. The private magnet 123 of the switch F, unlike the selector E, is provided withv the usual spring 124 that is connected with the release magnet 248.

The connector switch H may also be of any suitable or approved type, and, as shown, is a modified form of the connector described in United States Letters Patent No. 813,176, granted March 13, 1906, to Keith, Erickson & Erickson. The connector switch shaft (not shown) like the first-selector switch shaft, carries the wipers 125 and 127. The connector switch is also controlled by the calling subscriber through the medium of the vertical and rotary line relays 128 and 129. The vertical line relay 128 directly controls the vertical magnet 130 and also the rotary magnet 131. The ofiice of the vertical magnet 130 is to give the shaft and shaft wipers their vertical motion, and the rotary magnet 131 imparts to the shaft and shaft wipers a rotary or circular motion. The rotary line rela 129 controls the private ma et 133 which, under certain conditions, 1n turn controls the vertical and rotary magnets 130 and 131, release magnet 134, and also the side switch wipers 135, 136, 138 and 139. The side switch of the connector, like the side switch of the first-selector, has a normal or irst posit-ion, a second position and a third position. The release magnet 134 is also controlled by a special release relay 132. The central oilice is equipped with busy-signaling apparatus of any suitable design comprising an interrupter in series with the primary winding of an induction-coil as shown at N, whereby a busy-signaling current is induced in the secondary winding 260 of the said coil.

The line switch I (Fig. 3) is a modification of the line switch C (Fig. 1), and is bridged across the trunk conductors 192 and 193. Like the switch C it is equipped with the trip magnet 140 for operating the plunger arm 146, as explained 1n connection with the line switch C. Also the usual release magnet 141 provides thef means for restoring the switch to normal position. In this switch the cut-olf relay 144 is provided with only two springs, namely 142 and 143, Mich are arranged so that when the trip magnet energizes and permits the plunger to seize an idlev trunk, the bushing 145 on the end of the plunger arm 146 then carries the spring 142 out. of engagement with the spring 143, thus breaking the circuit of the trip magnet 140. The plunger arm 146 is similarto Athe plunger arm 45 of the line switch VC (Fig. 5), and in addition to the arrangement shown in Fig. '5 the bushing 145- is provided for operatin the springs 142 and 143, as explained. e line switch K which is the terminal of the trunk line, the conductors 192 and 193 of which line are shown,.is a modification of the switch C, and comprises the usual trip magnet 147 and the release magnet 148, but the bridgecut--oil relay is omitted. Both of the line switches K and C being allotted to the line of substation A', the switch K may be termed the incoming switch and the switch C' the outgoing switch, since when the substation A is called the line switch K is employed in establishing the connection, and when the subscriber at substation A calls another substation the line switch C is brought into service. It will be understood, of course, that the substation A (Fig. 1) is rovided with a switch similar to the swltch in which switch the normal conductors 93, 94 and 96a terminate, exactly as the conductors 266, 267 and 238 of the switch C' (Fig. 4) terminate in the switch K. It will also be evident that the conductor 95 of the switch C (Figs. 1 and 5) terminates in a connector bank, exactly as the conductor 207 of the switch lC' terminates in the bank of the connector H (Fig. 3).

A clearer' understanding of the operation of my improved system may be obtained by considerin its operation, when one subscriber cal another. Assume, for example, that the subscriber at substation A desires to call the subscriber at substation A to which is allotted the line #2220. To call the number 2220 the subscriber at substation A raises his receiver fromthe switch-hook and operates the calling device once, in the well-known manner for each d' it. When the dial is rotated for the first lgit a preliminary impulse is transmitted over the rota line conductor. This preliminary imp se energizes the trip ma et 47, wherey the line switch is operate to seize an idle trunk line leading to a rst-Selector. The dial in returning to normal position for the first di 't operates the, first-selector switch to esta lish connection with an idle trunk line leading to a second-selector. The second selector F, in asimilar manner, operates in accordance with the second digit to select an idle trunk line leadin to a secondary line switch. When the dia is rotated for the third digit this secondary line switch receives a preliminary impulse and is tri pedin or operated to seize an idle trun liv leading to a connector switch H, in the same manner in which the first line switch C is operated to seize a first-selector switch. It will be understood, of course, that when the dial is turned for each digit a preliminary rotary im ulse is transmitted to the rotary line, whic impulse, if a selector E or F or-a connector H is on the line, is received b the rotary line relay of the switch while tiile side switch is in first position. This rotary line relay, of course, energizes; but since the side switch is locked in first position until the shaft is raised, is without effect and the switch is not operated until the dial delivers the vertical impulses. Said preliminary impulse is eiective only in operating the line switches. The impulses for the ast two digits are directed toward the connector H which operates to place its shaft wipers in connection with the contacts corresponding to the desired line, and when this connection is made the master switch M line con is operated to carry the plungers of all idle switches K opposite the trunk line leading to the particular line switchI previously Selected by the selector F. When the plungers are carried to this position the line switch K is trip ed into connection with the trunk dnctors 192 and 193, and the connector H automatically released, whereby the conductors from the second-selector are extended directly through the line switch K to the called substation. From this it will be evident that the connector switch H merely serves to operate the line switch K, so that the conductors from the second-selector are extended to the calling substation directlv through the line .switch K, and not throug a connector.

The preliminar im ulse for operating the line switch which occurs when the calling subscriber rotates the dial in a forward direction for the first digit, is caused by the rotary impulse s ring 24 being pressed against the groun post 20. As a result of the impulse the trip magnet 47 of the line switch C is energized by a flow of culrent from ound G to the springs 18 and 19, groun post 20, impulse spring 24 to the rotary line conductor 32, conductor 153, cut-ofi' relay springs 154 and 155 to.

the trip ma et47 thence through said tri magnet to t e con uctor 156, springs 86 an 85, through the winding of the motor magnet 71 to the battery lead 160, thence through battery B to round G. Althou h this circuit includes t e motorl magnet g1 this magnet 71 does not operatively energize, since the magnet 47 is of much higher resistance than the magnet 7,1. As soon as the trip magnet 47 energizes, the armature 51 is attracted and the plunger 44 is liberated and thrust into the bank terminal Q by the spring 58, assuming that the plunger 44 is opposite the terminal Q at the time. When the plunger 44 engages the bank terminal Q an energizing circuit is closed through the motor magnet relay 73, which in turn operates .to close an energizing circuitthrough the motor magnet 71. The motor magnet then operates to advance all idle plungers which are in enga ement with the shaft opposite the next id e bank terminal similar to the terminal Q. The circuit through the relay 73 extends from ground Gr2 through the Winding 161 of the relay 73, segment 74, wiper arm 75, segment 84, conductor 162, bank terminal springs 7 0 and 69, release magnet 48 to the battery lead 160, thence through battery B to ground G. Although this circuitincludes the release magnet 48 the magnet 48 does not operatively energize, since the windings of the relay 73 are of a high resistance, while the winding of the release magnet is comparatively low. The relay 73 upon energizing` operates to place the springs 87 and 88 in conllt) tor magnet.

tact, whereby a circuit is completed through the motor magnet 71 extending from ground G through the sprin s 88 and 87, motor magnetsprings 86 an 85, through the motor magnet 71 to the battery lead 160, thence through battery B to ground G. The motor magnet 71 upon energizing attracts its armature 81 whereby the pawl 82 engages the ratchet wheel 72 and rotates the wheel one step. When the armature 81 is attracted against the magnet cores the springs 85 and 86 disengage, thereby breaking t e energizing circuit through the mo- The cam 76 being in engagement with the pin 77 is operated to advance the plunger shaft 60, and consequently all idle plungers that maybe in normal condition with the shaft 60, one step and to a point-opposite another trunk terminal similar to the terminal Q, assuming the next succeeding trunk is idle. Consequently, `the wiper 75 1s carried from the contact point 84, which corresponds to the terminal Q, to the contact point 89, which latter corresponds to the terminal before which the advanced idle plungers are now resting. Su pose that nine subscribers have called, an that the master switch has been thus operated nine steps, carrying the wiper 75 to the last contact point 164. Now when the motor magnet 71 operates for the last step, when the tenth subscriber calls, the wiper 75 moves back and drops into engagement with the contact polnt 84,as already explained. If the first trunk 1s still busy the wiper 75 finds a potential on the contact 84, and an ener izing circuit is established through the dlfl'erential relay 73, which in turn operates to close an energizing circuit through the motor magnet 71. The current through the said relay 73 Hows from the said contact 84 through the wiper 75 to the common segment 74, through the winding 161 of the differential relay 73 to v ground G. When the differential relay 73 attracts its armature the differential relay sprin 87 and 88 are pressed into contact, t ere y closing an energizing circuit for the motor ma et 71 from ground Gr3 through the sai springs 88 and 87, through the motor magnet springs 86 and 85, motor ma et 71, thence to the battery lead 160, an through battery B to ground G. The motor magnet then operates, as previously explained, to rotate the ratchet wheel 72 one step for advancing the plunger shaft 60 one step, and the master switch bank Wiper 75 one step also, and into engagement with the second segment 89. The plunger shaft 60, when thus advanced one step, carries all idle plungers that are in engagement with the said shaft op osite the next bank terminal, as previous y explained.

If there should still be a guarding potential at the bank segment 89 the master switch bank the dierential relay 73 will remain energized, whereby the energizing circuit through the motor magnet 71 is again com- A through the differential relay 73 1s broken,

at which time the said relay in turn breaks the energizing circuit for the motor magnet 71, until the next subscriber makes a call. At the instant that the plunger 44 enters the said bank terminal Q the following springs are pressed into contact: 63 and 64, 65 and 66, 67 and 68, and 69 and 70. Theengagement of the springs 67 and 68 closes a circuit through the cut-ofi' relay 46 extending from ground G4 through the springs 68 and 67, conductor 163, relay 46 to the battery lead 160, thence through battery B to ground G. The said relay upon energizing breaks the-contact between the springs 154,

155 and 157, whereby the vertical and rotary line conductors 31 and 32 become disconnected from the trip magnet 47. The cutoff relay upon energizing places the springs 158 and 159 in contact, thereby establishing a guarding potential by way of the normal conductor 95 to the connector private bank contacts corresponding to the line that terminates in the line switch C, to prevent any subscriber from calling the said line after the calling subscriber at substation A operates his dial preparatory to making a call, as explained. The circuit over which the said guarding potential is established extends from ground Gr15 `through the springs 159 and 158 to the private normal conductor 95. Also, the closure of connection between the springs 69 and 70 establishes a guarding potential at the master switch bank contact 84 over the following circuit: from battery B to the battery lead 160, through the release magnet 48 and springs 69 and 70`over the conductor 162 to the said contact point 84. It will be understood that the bank terminal Q, being the iirst'bank terminal of the line switch bank, corresponds to the first segment 84 of the master switch bank O and, therefore, to the trunk line, the conductors 90, 91 and 92 of which terminate in the selector E. This guarding potential protects the seized trunk conductors 90, 91 and 92 from being seized by other plungers, as already explained. The closure of connection between the springs 63 and 64 extends the calling subscribers vertical line conductorl 31 to the vertical trunk conductor 90 and to the side switch wiper 100 of the rst-selector E. The closure of contact between the @rings 65 and 66 in a similar manner extends the subscribers rota line conductor 32 to the rotary trunk con uctor 91 and to the side switch wiper 101 of the selector E. l: The subscriber has thus established connection with the selector E which is now operated by the impulses that are sent in as the dial returns. The first digit being 2 the spring 23 is pressed onto the ground post twice. As a result the vertical line relay 1080f the lirst-selector E is energized each time by a vflow of current from the substation ground G through the springs 18 and 19 to the ground post 20, thence through the spring 23 to the vertical line conductor 31, line switch bank springs 63 and 64, vertical trunk conductor 90, side switch wiper 100 of the selector E, contact point 170, vertical line relay 108 to the battery lead 160, thence through battery B and to ground G. Each time that the vertical line relay 103 energizes, the line relay spring 111 is pressed onto the ground spring 110. The vertical magnet 96 is thereby energized and the wipers 119, 120 and 121 of the selector .E are raised to the second bank level opposite fthe first contact of said level. The energizing circuit for the said vertical magnet 96 extends from ground Gr5 through the springs 110 and 111, private springs 105 and 106 to the vertical magnet 96, thence to the battery lead 160 and through b attery B to ground G. The spring 24 is then pressed onto the ground post- 20, Grounding the rotary line conductor 32 an therefore, energizmg the rotary line relay 109 of the selector E. The energizing current passes from ground G to the rotary line conductor 32, thence it flows through the line switch bank springs and 66, rotary trunk conductor 91, side switch wiper 101 of the selector E, contact point 171 to the rotary line relay 109, thence to the battery lead 160, and through battery B to ground G.

The rotary line relay upon operating presses the line relay spring 12 onto the ground spring 110, thereby establishing a circuit through the private magnet 99 from ground G*5 through the springs 110 and 112 to the private magnet 99, and through the said magnet to battery lead 160, thence through battery B to ground G. The' private magnet upon energizing and de-energizing permits the selector side switch to pass from first to second position., perlnitting the side switch wipers 102 and 103 to engage the contact points 172 and 173, respectively. The closure of connection between the side switch wiper 102 and the contact oint 172 Sets up an energizing circuit for t e rotary magnet 97 from ground G6 to the contact point 172, through the side switch wiper 102, interrupter springs 107, rotary magnet 97 to the battery lead 160, and through battcry B to ground G. The said rotary magnet 97 then operates to rotate the wipers 119, 120 and 121 of the selector E into engagement with the first Contact of the second level of the selector banks, from which contacts it is assumed the trunk line conductors 175, 176 and 104 lead to the selector F. It the first trunk is busy, however, the wipers have to pass over busy trunk lines, and then as soon as the private wiper 121 engages the first grounded private bank conta-ct point, the private magnet 99 energizes again, locking the side switch 'in second position. The el'lergizing'circuit forsaid private magnet extends frorn the grounded terminal G of bat tery B through an occupying switch (not shown) to the private wiper 121, thence over the conductor 174 and through the backrelease relay 115 to the side switch wiper 103, contact point 173, private magnet 99, thence through said magnet to the battery lead 160, and through battery B to ground G. The private magnet 99 upon thus be coming energized locks the side switch wiper 102 in engagement with the grounded contact point 172, whereby the rotaryl magnet 97 will be energized intermittently untilthe wipers are carried beyond the last busy trunk line. At the instant that the private wiper leaves the last busy Contact point the energizing circuit throughl the private magnet 99 is destroyed, and as a result the selector side switchpasses to third position. It, however, there are no busy trunk lines, the armature of the rotary magnet 97 releases the side switch to third position as soon as the Wipers are carried into engagement with the first trunk line. As soon as the side switch passes to third position, as stated, the

subscribers line conductors 31 and 32 are extended to the conductors 175 and 176, which in this case, it is assumed, lead to the selector switch F. The extension of the line occurs, of course, as soon as the side switch wipers 100 and 101 enga e the contact points 177 and 178, respective y. Not only 1s the subscribers line thus extended, but a guarding potential is also established at the pri vate wiper 121, when the side switch wiper 103 passes onto the grounded contact poin 179, for protecting the seized trunk line from interference by other calling subscribers. This guarding potential extends from ground G' to Contact point 179, thence through the side switch wiper 103, back-re lease relay 115, and conductor 17 4 to the private wiper 121. It will be evident, of Course, that the energizing circuit for the rotary magnet 97, to which reference has already been made, is destroyed, whenthe idle trunk line is seizedthat is, when the side switch wiper 102 leaves the contact point 172. The second digit of the called number being 2, the calling subscriber operates his dial accordingly, as a result grounding the vertical line conductor 31 when the spring vline switch bank s side switch wiper 4vertical line relay step by step nector H.

23kmeets the ground post 20. The vertical line relay 188 of the switch F is, therefore, energized twice by a iow of current from the substation ground G t0 the vertical line conductor 31, thence through the rings 63 .and y werti'cal trunk con neto-r y90, thence to the 100 of the selectorE, contact point 177, vertical line wiper 119, vertical trunk conductor 175, side switch wiper 187, vertical line relay 188 to the battery lead 160, thence through battery B to ground G. That is, when the vertical line conductor 31 is grounded for the secondldigit the 188 operates to close a circuit through the vertical' magnet 264, which operatesv to carry the 4shaft wipers to ay point opposite the bank terminals of the second level. Whew the rotary line conductor 32 is grounded after the vertical impulses the rotary line relay 206 is ener ized, whereby an energizing circuit is esta lished through the private magnet 123, which in turn operatesin the usual wayto release the'side switch, as described in connection with switch l. l

After the switch F comes to rest its shaft wipers 189 and 190 are in engagement with the trunk conductors 192 and 193, respectiyely, which lead to the line switch 1 (Fig. 3 protecting potential at the contact 194 for guarding the seized trunk line. Furthermore, the trunk conductors 192 and 193 terminate in thebank of the line switch K. Now, when the dial is turned clockwise for the third digit the preliminary rotary impulse, as previously explained, energizes the trip magnet 140 which operates, as explained in connection with the line vswitch C, to seize a trunk line leading tothe con- The energizing circuit of the trip magnet 140 extends' from the substation ground G' to the rotary line conductor `32, trunk conductors 91, 176 and 193 to the conductor 165 (Fig. 4), then to the conductor 165 Fig. 3), through the cut-oli springs 142 and 143, through the trip magnet 140 to the motor magnet springs 166 and 167, through the motor magnet 168 to the battery lead 160, and throughv battery B to ground Gr. The trip magnet upon energizing operates to permit the plunger arm 146 to trip-in, whereby the springs -180 and 181, 182v and 183, 184 and 185, and 186 and 187a engage.v When the plunger arm 146 operates, the cuto spring 142 is carried out of engagement with the spring 143 by the bushing 145 upon the end of the plunger arm 146. The disengagement of these springs cuts oli the conductor 165 from the trip magnet 1.40. When the springs 182 and 183 are carried into engagement by the plunger of the switch I, an energizingcirf cuit is established through the motor relay ythe master switch J,

.is wound to a high resistance,

vly low resistance.

upon energizing operates the plunger shaft,

The'private wiper 191 establishes av post 20 twice,

. vertical line relay 128.

'conductor' 152, springs lsteps andV brought opposite,

is the private normal busy, either by vswitch M of the group k195 of the master switch J. This circuit extends from ground Gr8 through the said relay, common segment 196 of the bank of segment 198, then through the bank springs 183 and 182, through the lwinding ot the release magnet 141 to the vbattery lead 160, land through battery B to ground G. The relay 195 now to close the springs 199 and 200 in Contact` whereby an energizing circuit is clo through the motor magnet 168. Although the release magnet 141is included in thefen- 195'it does not operate, since the relay195 while the rewound to a comparative- The motor magnet-168 lease magnet 141 is as explained in connection with the line switch C and the master switch D, to carry the engaging plungers opposite the Vnext `idle trunk line which leads to asecond conl nector switch. When the bank springs 180 and 181, and 186 and -subscribers line conductors 31 and 32 are 187 a engage, the calling extended to Vthe connector trunk conductors 201 and 202. The ground impulses from the substation to the line conductors for the last two digits-namely the third and fourth-are directed toward the connector H. For the third digit 2 the' vertical impulse spring 23 is pressed onto the ground whereby an energizing circuit is closed eachv time through the connector This'circuit extends from ground G through the ground post 20, spring 23, line conductor 31, springs 63 and wiper 197 to the energizes and operates v- .ergizing circuit of the motor magnet relay"` and 64, trunk conductors 90, 175 and 192.

180 and181, vertical line relay 128 to the battery lead 160, thence through battery B to'ground G. Each time that the vertical line relay 128 is energized the line relay springs pressedintlfcontact, thereby closing an energizing circuit each time through the vertiical magnet 130 which operates 1n the usual manner one ste Y at a time. The shaft the level in located the terminals of the conwhich are 'ductors 205 and 207 that lead to the incoming and outgoing line switches of the called 203 .and 20.4 are A wipers 125 and 12 are, therefore, raised two line. Of these conductors' the conductor 207 f' i' conductor and leads directly to the spring 243 of the bridgeecutofi' relay 236 of the outgoing line switch C. This conductor'is adapted "to be grounded and maintained so when the 'line"#2220 is being called or by calling. The conductor 214 may be termed themaster switch starter and leads to the. master ing individual switch through the motor starter relay 213 to to which the incom- K belongs, ipassing 176 and 193 being the `previously describe =l1ne rela switch When the connector side to third position it will be he release re- H, thus causing the relay 132 to energize, yreleasing both t e connector H and the line switch I and, at the same time, trippin the incoming individual switch K of the Fine #2220 by sen ground impulse over the remainthe said conductors, namely the conductor 205, throu h the said trip magnet 147 to the non-grouned terminal of battery. After the connector shaft has heen raised the vertical impulses, the rotary impulse is sent in for the third digit. This is done when t rotary impulse spring 24 makes Contact with the ound post 20, thereby circuit through the line conductor 32, trunk conductors 91, conductor 165, springs 186 and 187, throng the rotary line relay 129 to the battery lead 160, thence through battery B to ground G1.' e rotary line relay upon operating c oses an ene zin through the private magnetri33, igvhich o Braten to release the connector side m tiratto second position. The last digit calling device is operated, as d, grounding the vertical conductor 31 ten times and the rotary line conductor 32 once. The vertical and rotary 128 and 129 are operated over previou y traced ci-rcuits. However, when e line relay s rings 203 and 204 engage, a circuit is cl through the rotary magri `131 instead o f through the vertical magnet Each time that the rotary energized it operates to rotate the shaft wipers 125 and 127 one step at a time until the said wipers are carried into engagement with the conductors 205 and 207 which are allotted to the line of substation e energizing of the 129, as previously stated, completes an enering circuit through, the private magnet 13 which from second to magnet is shaft and third position, thus placing the side switch wipers v133, 136, 138 and 139 in contact with their respective contact points. When the side switch wiper 1,35 en the contact point 208 a ground potenti is established at the bank contact of the master switch M (Fig. 4) correspondby means of this conductor the vground G at the conductor vsprings 185 lsegment 2114 at the master switch bank, Fig.

v133 to the battery lead 160,

- 218, motor post and spring circuit l Vrelease relay 132 and rotary line relay now operates to release the side ie,sie

`ing to the conductors 192 and 193 of the trun line.

ispotential extends from H through the release relay 132, contact point 208, side switch lwiper 135, conductor .209, bank and 184, conductor 210 to the e side switch wiper 136 upon engaging the contact point 212 closes an energizing circuit through the motor magnet relay 4) extending from ground Cr1o battery B to ground G. The relay 213 energizes and laces the springs 217 and 218 in contact, w ereby an energizing circuit is closed through the motor magnet 221 from ground G11 through the springs 217 and magnet interrupter springs 219 and 220, throu h the motor magnet 221 to the battery lea 160, and through battery B to ground G. s long as the connector H remains with the side switch wi Position the ay 213 is maintained, ergizing circuit through the motor magnet 221. e motor magnet continues tooperate, rotating the ratchet wheel 222 already described, is grounded through the closed through the release re ay 132. This cir- H through the relay 132 and side switch wiper 135, as explained, to the segment 211, then through the wiper 223 to the common segment 224, thence to battery lead 160, and through battery B to ground G. The relay 132 upon energizing operates to release the connector switch H and also the line switch I. N ow when the connector releases, the and 136 then leave points 208 and 212, e energizing circuits through the through the motor magnet relay 213 are broken. The energization of the release relay 132 not only releases the connector switch H and the line switch their respective contact whereby th 226 and'227 to separate. It will be understood, therefore, that the releasing of the connector switch H and of the line switch I occurs as soon as the wiper 223 of the masiio 

